The paper reports work studying the association of benzo[a]pyrene (BaP), pyrene, 3,3,4,4-tetrachlorobiphenyl (TCB) and 2,2,4,4-tetrabromo diphenyl ether (TBDE) with natural dissolved organic matter (DOM). The aim was to determine the essential characteristics that predict the sorption capacity of DOM for hydrophobic contaminants. Samples had been collected from natural waters at five Nordic sites during autumn 1999 and spring 2000, isolated by reverse osmosis and thoroughly characterized. Generally, bioavailability of BaP and pyrene to D. magna reflected the measured association of the compounds with DOM. The data emphasize the importance of aromaticity of DOM, estimated by simple spectroscopic methods, in predicting sorption capacity for polycyclic aromatic hydrocarbons. The situation with halogenated compounds still remains unclear.